1. Field of the Invention
The present invention relates to a method for fabricating a semiconductor device, and more particularly to a method for fabricating a silicide film on the upper surface of a silicon substrate.
2. Description of the Background Art
In order to lower the contact resistance when fabricating a semiconductor device, generally a silicide film, a low resistant material is formed at the contact portion between conductive layers. Especially, a titanium silicide film which has a relatively low resistance compared to that of other silicide, is drawing much attention as a wiring material.
A conventional method for fabricating a titanium silicide film typically employs a self-alignment method. In such a method, a titanium film is deposited on a silicon film by a physical vapor deposition (PVD) and subject to a thermal treatment causing a silicide reaction between titanium and silicon, thereby forming a titanium silicide film.
The conventional method for fabricating a titanium silicide film by the self-alignment method will now be described with reference to the accompanying drawings.
FIGS. 1A and 1B illustrate a fabricating process of a silicide film in accordance with a conventional art.
As shown in FIG. 1A, a titanium film 11 is formed on the upper surface of the silicon layer 10.
Next, the titanium film 11 is subject to thermal treatment at the temperature of about 650xc2x0 C. Then, as shown in FIG. 1B, the silicon layer 10 and the titanium film 11 are reacted to form a titanium silicide layer 12.
However, during the thermal treatment for forming the titanium silicide film by the self-alignment method, an impurity, such as oxygen, permeates into the titanium film, causing agglomeration of silicide.
In order to solve such a problem, a process has been developed and commercially used in which a titanium nitride (TiN) is deposited on the titanium film and thermally treated.
However, in such conventional method in the event that the titanium silicide layer is formed in a contact hole having a high aspect ratio, the titanium film step coverage characteristic is degraded when formed by the physical vapor deposition method.
Especially, since the titanium film is not deposited on the bottom of the contact hole and thickly deposited at the entrance of the contact hole, the entrance of the contact hole is clogged.
In addition, the method for fabricating the titanium silicide film by the self-alignment method limits the thickness of the film to be formed and the titanium silicide film fabricated by the self-alignment method has a low thermal stability.
In order to solve such problems, a method for forming a titanium silicide film by using a Plasma Enhanced Chemical Vapor Deposition has been recently proposed.
That is, a titanium silicide film is deposited by reduction between TiCl4 and silane gas. A reaction formula for forming titanium silicide is as follows.
TiCl4+2SiH4xe2x86x92TiSi2+HCl+2H2 
Though the Plasma Enhanced Chemical Vapor Deposition has a favorable bottom coverage characteristic, it also has the following shortcomings.
When a titanium silicide film is formed on the upper surface of a silicon substrate by using Chemical Vapor Deposition, the silicon substrate is etched due to HCl, a by-product of the reaction of TiCl4 and silane gas, a source gas. This results in an uneven interface between the silicon substrate and the deposited titanium silicide film.
In addition, its junction depth is reduced, causing increase in a leakage current.
Moreover, as the doping concentration at the interface of the semiconductor substrate (silicon) and the titanium-silicide film is reduced, contact resistance is increased.
Furthermore, since the process of depositing the titanium silicide film by using the plasma enhanced chemical vapor deposition method is conducted at a high temperature, the silicide reaction occurs rapidly, so that when the titanium silicide is deposited, the agglomeration phenomenon also occurs thereon, resulting in a rough interface between the silicide and the silicon substrate.
Therefore, the present invention provides a method for fabricating a titanium silicide film so that when the film is fabricated by using a Chemical Vapor Deposition, an NH3-gas or an N2-gas plasma process is performed several times, thereby minimizing etching of the silicon substrate and consuming of a dopant of an impurity layer, restraining an increase in leakage current.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a method for fabricating a titanium silicide film including the steps of: a) depositing a titanium silicide film as thick as {fraction (1+L /n)} of a total desired thickness on a silicon substrate by using the Chemical Vapor Deposition method; b) processing the titanium silicide film with a nitrogen-gas plasma or an ammonia-gas plasma; and c) repeatedly performing process a) and b) for xe2x80x98nxe2x80x99 times.
In the above method, the step of processing the titanium silicide film with a nitrogen-gas plasma or an ammonia-gas plasma refers to a process of forming a nitride film of less than 100 xc3x85 in thickness on the upper surface of the titanium silicide film.
In the above method, step a) and step b) are performed in the same apparatus.
In the above method, before performing step a) the following steps are sequentially performed, forming an impurity layer by ion-implanting the silicon substrate, forming an insulation film on the silicon substrate, and partially etching the insulation film to expose the upper surface of the impurity layer, thereby forming a contact hole.